The dehydration reactions of alcohols to produce alkenes have been known for a long time. Solid acid catalysts are widely used for alcohol dehydration and the conversion of alcohols therewith is nearly complete. However, in view of the potential downstream applications of olefins, it is of particular importance to limit the amount of secondary products and insure a stable catalyst performance to gain in process efficiency and to save expensive steps of downstream separation/purification as well as to recover the catalyst activity by regeneration.
Dehydration of ethanol was described in WO2011/089235. The process for the dehydration of ethanol to ethylene was carried out in presence of zeolite catalysts and provides an alternative route to ethylene from biobased products if ethanol is obtained by fermentation of carbohydrates.
Dehydration of isobutanol to corresponding olefins brings a perspective route to produce the renewable feedstock for petrochemicals and refining applications. Unfortunately, the direct conversion of isobutanol over a conventional dehydration catalyst, for example on alumina, leads to a product rich in isobutene. Not isobutene but linear butenes are often interesting as feedstock for metathesis, sulfuric acid catalyzed alkylation, oligomerization, oxidative dehydrogenation to butadiene, for the use as a co-polymer or for the integration into the Raffinate I-pool. The definition of Raffinate I shall be found in U.S. Pat. No. 4,282,389 (column 1 lines 41-46). Therefore, one-pot process converting isobutanol to the effluent rich in the linear butenes is seeked.
While many skeletal isomerisation catalysts for the conversion of n-butenes into isobutene have been developed, the reverse skeletal isomerisation of isobutene into n-butenes has been rarely mentioned. Among the catalysts being active and selective, there are mostly unidirectional 10-membered ring zeolites. WO2011/113834 relates to the simultaneous dehydration and skeletal isomerisation of isobutanol on acid catalysts. The process discloses the contact of a stream comprising isobutanol with a catalyst able to make such reaction. The catalyst was a crystalline silicate, a dealuminated crystalline silicate, or phosphorus modified crystalline silicate having Si/Al higher than 10; or silicoaluminaphosphate molecular sieve, or a silicated, zirconated or titanated or fluorinated alumina. The conversion of isobutanol was almost complete with selectivity in butenes ranging from 95 wt % to 98 wt %. The selectivity in isobutene was around 41-43%. This document clearly states that steaming at temperature above 400° C. leads to a modification of the acidity of the catalyst and to the removal of aluminum from the crystalline silicate framework. Subsequently, it is necessary to treat the catalyst via a leaching to remove the aluminium and to increase the ratio Si/Al. The steps of steaming and leaching are associated in this document.
However, crystalline silicate catalysts deactivate fast and have limited regenerability. Hence, there is still a need for selective catalysts towards linear olefins and having improved regenerability.
In catalysis letters 41 (1996) 189-194, Gon Seo et al. studied the impact of coke deposits on ferrierite zeolites for the reaction of skeletal isomerization of 1-butene. The ferrierite studied was calcined at 500° C. for 16 h without any other particular treatment aiming at modifying its acidity. This ferrierite has a Si/Al ratio of 21 and it is further covered with coke using a plasma deposition before the reaction of skeletal isomerization of 1-butene is studied.
In WO2013/014081, SUZ-4 is studied for the methanol to olefin reaction. This document discloses the possibility of steaming the catalyst at a temperature of at least 400° C. followed by a leaching i.e. a washing of the steamed solid with an aqueous acid solution. Such treatment are said to increase the Si/Al ratio.
In Applied Catalysis A: General 208 (2001) 153-161, Rutenbeck et al. studied the skeletal isomerization of n-butenes to iso butene. The catalyst studied was a ferrierite having a Si/Al ratio in the range of 20-70. A treatment of the ferrierite with the inorganic acid HCl was performed to obtain the protonic form of the ferrierite.
In the Journal of Catalysis 163, 232-244 (1996), Wen-Qing Xu et al. studied the modification ferrierite for the skeletal isomerization of n-butene. The ferrrierite used presents a Si/Al ratio of 8.8. Treatment of the ferrierite also includes steaming at a temperature of at least 550° C. and acidic treatment with HCl or HNO3.
In EP2348005, the use of a ferrierite based catalyst for the dehydration of isobutanol is described. It is disclosed that the ferrierite may be used directly without further treatment or that it may be used once being steamed and dealuminated with an acidic treatment.
In Applied Catalysis A: General 403 (2011) 1-11, Dazhi Zhang et al. described the use of a ferrierite for the conversion of n-butanol to iso-butene. Such ferrierite was calcined at 550° C. but did not undergo any further treatment. The ferrierite used are commercial products: CP914 and CP914C from Zeolyst International.
In U.S. Pat. No. 5,523,510, the use of a acid wash ferrierite based catalyst for the skeletal isomerization of n-olefins to iso-olefins is described. Such acid wash is performed with HCl. In all the examples, the ferrierite is firstly steamed before being acid wash.
The present invention aims at providing catalyst compositions that address the above-discussed drawbacks of the prior art.